1. Field of the Invention
This invention relates to an acceleration/deceleration control method for a numerical control device (CNC) which subjects a pre-interpolation tangential velocity command value to an acceleration/deceleration control, and more particularly, to an acceleration/deceleration control method for a numerical control device by which an increase in the machining time caused by the acceleration/deceleration control is reduced to a minimum permissible value.
2. Description of the Related Art
In numerical control devices (CNC), an instructed tool feed speed is automatically subjected to an acceleration/deceleration control to achieve a smooth starting operation and stopping operation, and further, to ensure a change of the feed speed when required.
In the conventional acceleration/deceleration control method, a post-interpolation acceleration/deceleration control is effected for post-interpolation feed speeds of individual axes, by using predetermined accelerations, but this method has a drawback in that an actual path may be deviated from the instructed path because of a delay caused by the acceleration/deceleration control when corner portions of a path are continuously machined, to thereby cause an error in the machined shape.
To eliminate the above drawback, a pre-interpolation acceleration/deceleration control method has been developed and put to practical use. In the pre-interpolation acceleration/deceleration control method, a pre-interpolation feed speed, i.e., the feed speed in a tangential direction of the command path, is subjected to the acceleration/deceleration control, and no error occurs in the machined shape due to a delay caused by the acceleration/deceleration control. Since the acceleration during the acceleration/deceleration control must be set in such a manner that it does not exceed the maximum permissible accelerations for the individual axes, it is set to a constant value equal to the permissible acceleration of an axis having a minimum permissible acceleration, taking into account a worst case wherein the direction of the feed command is parallel to the axis having a minimum permissible acceleration, for example.
Nevertheless, where the feed direction is not parallel to the axis, the actual acceleration of the axis becomes smaller than the permissible acceleration, and thus the performance of the machine cannot be fully utilized and the machining time is unnecessarily prolonged.